The addition of two hydroxy groups in a cis manner to the carbon-carbon double bond of an alkene, as shown in FIG. 1, is an important transformation in organic synthesis. The resulting cis-1,2-diol products are versatile building blocks for pharmaceutical products and fine chemicals.
Traditionally, cis-dihydroxylation can be performed using stoichiometric amounts of osmium tetroxide or potassium permanganate (see: Haines, A. H., in Comprehensive Organic Synthesis; Trost, B. M.; Fleming, I. (eds.) Pergamon: Oxford, 1991; Vol. 7, p. 437). However, an immediate drawback is that these processes produce a large amount of toxic effluent. Furthermore, osmium tetroxide is highly toxic and very expensive, which hampers its use in large-scale synthesis. For the use of permanganate as oxidant, the reaction usually produces undesired over-oxidized products, and yields are lower than with osmium tetroxide.
Catalytic systems for alkene cis-dihydroxylation have been extensively pursued. In particular, development of osmium-catalyzed alkene dihydroxylation and its asymmetric variants represents an important milestone in modern organic synthesis [see: (a) Johnson, R. A.; Sharpless, K. B. In Catalytic Asymmetric Synthesis; by Ojima, I. 2nd ed., VCH: New York, 2000. (b) Kolb, H. C.; Van Nieuwenhze, M. S.; Sharpless, K. B. Chem. Rev. 1994, 94, 2483]. Several secondary oxidants including metal chlorates (see: Hofman, K. A. ChemBer. 1912, 45, 3329), hydrogen peroxide (see: Milas, N. A.; Trepagnier, J.-H.; Nolan, J. T.; Iliopolus, J. Ji. J. Am. Chem. Soc. 1959, 81, 4730), tert-butyl hydroperoxide [see: (a) Sharpless, K. B.; Akashi, K. J. Am. Chem. Soc. 1976, 98, 1986. (b) Carlsen, P. H. J.; Katsuki, T.; Martin, V. S.; Sharpless, K. B. J. Org. Chem. 1981, 46, 3936. (c) Webster, F. X.; Rivas-Enterrios, J.; Silverstein, R. M. J. Org. Chem. 1987, 52, 689. (d) Martin, V. S.; Nunez, M. T.; Tonn, C. E. Tetrahedron Lett. 1988, 29, 2701 (e) Caron, M.; Carlier, P. R.; Sharpless, K. B. J. Org. Chem. 1988, 53, 5185], N-methylmorpholine N-oxide (NMO, Upjohn process) [see: (a) Schneider, W. P.; McIntosh, A. V. U.S. Pat. No. 2,769,824 (1956). (b) Van Rheenen, V.; Kelly, R. C.; Cha, D. Y. Tetrahedron Lett. 1976, 17, 1973] are known for effective catalytic cis-dihydroxylation reactions. For sterically hindered alkenes, the catalytic system employing trimethylammonia N-oxide as secondary oxidant has been reported to give improved product yields (see: Ray, R.; Matteson, D. S. Tetrahedron Lett. 1980, 21, 449).
To overcome problems of over-oxidation and inertness towards sterically hindered alkenes, catalytic system using hexacyanoferrate(III) as secondary oxidant has been developed (see: Minato, M.; Yamamoto, K.; Tsuji, J. J. Org. Chem. 1990, 55, 766). Consequently, an enantioselective version based on hexacyanoferrate(III) as oxidant was developed by Sharpless and co-workers (see: Ogino, Y.; Chen, H.; Kwong, H. L.; Sharpless, K. B. Tetrahedron Lett. 1991, 32, 3965). Currently, the “K2[OsO2(OH)4+K3[Fe(CN)6]” formulation is commercially available and branded as AD-mix.
The search for transition metal catalysts alternative to osmium for cis-dihydroxylation of alkene is receiving current attention. Earlier work by Shing and co-workers showed that RuCl3.xH2O is an effective catalyst for cis-dihydroxylation of alkenes when using NaIO4 as oxidant with a mixture of acetonitrile, ethyl acetate and water as solvent at reaction temperature=0° C. [see: (a) Shing, T. K. M.; Tai, V. W.-F.; Tam, E. K. M. Angew. Chem., Int. Ed. Engl. 1994, 33, 2313. (b) Shing, T. K. M.; Tai, V. W. F.; Tam, E. K. M. Chung, I. H. F.; Jiang, Q. Chem. Eur. J. 1996, 2, 50. (c) Shing, T. K. M.; Tam, E. K. M. Tetrahedron Lett. 1999, 40, 2179]. Recently, Que and co-workers disclosed that alkene cis-dihydroxylation can be achieved with moderate selectivity using some iron complexes as catalyst and hydrogen peroxide as oxidant [see: (a) Chen, K.; Costas, M.; Kim, J.; Tipton, A. K.; Que, L. Jr. J. Am. Chem. Soc. 2002, 124, 3026. (b) Costas, M.; Tipton, A. K.; Chen, K.; Jo, D.-H.; Que, L. Jr. J. Am. Chem. Soc. 2001, 123, 6722. (c) Chen, K.; Que, L. Jr. Angew. Chem. Int Ed. 1999, 38, 2227]. In addition, Jacobs and coworkers reported that some manganese cyclic triamine complexes could convert alkene to its corresponding cis-1,2-diol in low yield using hydrogen peroxide as secondary oxidant (see: De Vos, D. E.; de Wildeman, S.; Sels, B. F.; Grobet, P. J.; Jacobs, P. A. Angew. Chem. Int. Ed. 1999, 38, 980).
At present, osmium-catalyzed alkene cis-dihydroxylation is still the system of choice because of its effectiveness and selectivity. However, recovery of the precious metal catalysts are difficult, and it may result in product contamination. This has restricted its use for large-scale reactions in industry. To this end, several research groups have already attempted to address the issues by heterogenization of the metal catalysts onto solid support[see: (a) Bolm, C.; Gerlach, A. Chem. Eur. J. 1998, 1, 21. (b) Salvadori, P.; Pini, D.; Petri, A. Synlett. 1999, 1181. (c) Gravert, D. J.; Janda, K. D. Chem. Rev. 1997, 97, 489. However, limited success was achieved with respect to recovery and reuse of the metal catalysts. For example, Kobayashi and co-workers recently developed a highly recoverable and reusable polymer-supported osmium catalyst for alkene cis-dihydroxylations using a microencapsulation technique (see: Kobayashi, S.; Endo, M.; Nagayama, S. J. Am. Chem. Soc. 1999, 121, 11229). A recent work by Choudary and co-workers reported that immobilized OsO42− on layered double hydroxides by ion-exchange technique was found to attain good recoverability and reusability for alkene cis-dihydroxylation (see: Choudary, B, M.; Chowdari, N. S.; Kantam, M. L.; Raghavan, K. V. J. Am. Chem. Soc. 2001, 123, 9220). Despite these advances, development of more easily handled metal catalysts with superior recyclability and catalytic activities is still highly desirable. A recent report by Park and co-workers showed that a 3-D networked osmium nanomaterial is an effective heterogeneous catalyst for dihydroxylation and oxidative cleavage of alkenes (see: Lee, K.; Kim, Y.-H.; Han, S. B.; Kang, H.; Park, S.; Seo, W. S.; Park, J. T.; Kim, B.; Chang, S. J. Am. Chem. Soc. 2003, 125, 6844).
Limited examples involving supporting transition metal catalysts other than osmium based complexes for alkene cis-dihydroxylation and alkene oxidative cleavage have been reported. Supported manganese cyclic triamine complexes converted alkenes to cis-diols when using hydrogen peroxide as oxidant, but poor yield and selectivity made this process impractical (De Vos, D. E.; de Wildeman, S.; Sels, B. F.; Grobet, P. J.; Jacobs, P. A. Angew. Chem. Int. Ed. 1999, 38, 980).
Application of nanosized metal particles as catalysts for organic transformations is receiving current attention [see: (a) Moreno-Mañas, M.; Pleixats, R. Acc. Chem. Res. 2003, 36, 638. (b) Roucoux, A.; Schulz, J.; Patin, H. Chem. Rev. 2002, 102, 3757. (c) Horn, D.; Rieger, J. Angew. Chem. Int. Ed. 2001, 40, 4330. (d) Bönnermann, H.; Richards, R. M. Eur. J. Inorg. Chem. 2001, 2455. (e) Rao, C. N. R.; Kulkarni, G. U.; Thomas, P. J.; Edwards, P. P. Chem. Soc. Rev. 2000, 29, 27. (f) Johnson, B. F. G. Coord. Chem. Rev. 1999, 190, 1269. (g) Bradley, J. S. In Clusters and Colloids: from Theory to Application; Ed.: Schmid, G. VCH: Weiheim, 1994; p. 459. (h) Lewis, L. N. Chem. Rev. 1993, 93, 2693. (i) Schmid, G. Chem. Rev. 1992, 92, 1709]. Due to its high surface area and the high density of active sites, nanosized metal particles exhibit superior catalytic activities versus the corresponding bulk materials.
Various synthetic methods for ruthenium nanoparticles have been reported in the literature. The reduction of ruthenium salts in polyol solution at evaluated temperature is promising and simple for ruthenium nanoparticles [see: (a) Viau, G.; Brayner, R.; Poul, L.; Chakroune, N.; Lacaze, E.; Fiévet-Vincent, F.; Fiévet, F. Chem. Mater. 2003, 15, 486. (b) Balint, I.; Mayzaki, A.; Aika, K.-I. J. Catal. 2002, 207, 66. (c) Miyazaki, A.; Balint, I.; Aika, K.-I.; Nakano, Y. J. Catal. 2001, 204, 364]. Besides, several research groups have developed some new preparation procedures for nanosized ruthenium particles. Chaudret and co-workers utilized the reaction of an organometallic ruthenium precursor under a hydrogen atmosphere in organic solvent to obtain a stable ruthenium colloid (see: Vidoni, O.; Philipport, K.; Amiens, C.; Chaudret, B.; Balmes, O.; Malm, J. O.; Bovin, J. O. Senocq, F.; Casanove, J. Angew. Chem. Int. Ed. Engl. 1999, 38, 3736). Also, Che and coworkers demonstrated that the solvothermal reduction of ruthenium salts is a viable route to nanosized ruthenium particles (see: Gao, S.; Zhang, J.; Zhu, Y.-F.; Che, C. M. New J. Chem. 2000, 739). In addition, Alonso-Vante and co-workers disclosed that highly dispersed nanocrystalline ruthenium particles could be prepared under mild conditions in an organic solvent from the ruthenium carbonyl precursor (see: Vogel, W.; Le Rhun, V.; Garnier, E.; Alonso-Vante, N. J. Phys. Chem. Chem. B 2001, 105, 5238). Furthermore, Lee and coworkers reported that nanosized ruthenium particles could be prepared by the sodium borohydride reduction of ruthenium chloride and ruthenium hydroxide (see: Lee, D.-S.; Liu, T.-K. Journal of Non-Crystalline Solids, 2002, 311, 323).
The reports on the catalytic reactivity of these ruthenium particles are, however, sparse in the literature. Miyazaki and co-workers reported alumina-supported ruthenium nanoparticles have a high reactivity for ammonia synthesis [see: (a) Balint, I.; Mayzaki, A.; Aika, K.-I. J. Catal. 2002, 207, 66. (b) Miyazaki, A.; Balint, I.; Aika, K.-I.; Nakano, Y. J. Catal. 2001, 204, 364]. Wakatsuki and coworker disclosed that TiO2-supported ruthenium nanosized metal particles exhibited the reduction of SO2 and H2 to give element sulfur (see: Ishiguro, A.; Nakajima, T.; Iwata, T.; Fujita, M.; Minato, T.; Kiyotaki, F.; Izumi, Y.; Aika, K.-I.; Uchida, M.; Kimoto, K.; Matsui, Y.; Wakatsuki, Y. Chem. Eur. J. 2002, 8, 3260). Schmid and co-workers revealed that ruthenium nanoparticles included in nanoporous alumina membranes catalyzed alkene hydrogenation (see: Pelzer, K.; Philippot, K.; Chaudret, B.; Meyer-Zaika, W.; Schmid, G. Zeitschrift fur anorganische und allgemieine chemie, 2003, 629, 1217). U.S. Pat. No. 6,551,960 discloses the fabrication of supported nanosized ruthenium catalyst and its reactivity for methanol reformation. Chan and co-workers reported that Ru—Pt nanoparticles, prepared by water-in-oil reverse micro-emulsion, displaced high catalytic activity for methanol oxidation when supported on carbon electrode (see: Zhang, Z.; Chan, K.-Y. Chem. Mater. 2003, 15, 451). Recently, it was reported that zeolited-confined nanosized ruthenium dioxide can efficiently promote aerobic oxidation of alcohols (see: Zhan, B.-Z.; White, M. A.; Sham, T.-K.; Pincock, J. A.; Doucet, R. J.; Rao, K. V. R.; Roberson, K. N.; Cameron, T. S. J. Am. Chem. Soc. 2003, 125, 2195). However, the reactivities of ruthenium nanoparticles toward cis-dihydroxylation and oxidative cleavage of alkenes are hitherto unknown in the literature.
Ruthenium salts and complexes are known to be versatile catalysts for various oxidative transformations [see: (a) Murahashi, S.-I.; Komiya, N. In Biomimetic Oxidations Catalyzed by Transition Metal Complexes; Ed.: Meunier, B.; Imperial College Press, 2000; p. 563. (b) McLain, J. L.; Lee, J.; Groves, J. T. In Biomimetic Oxidations Catalyzed by Transition Metal Complexes; Ed.: Meunier, B.; Imperial College Press, 2000; p. 91. (c) Ley, S. V.; Norman, J.; Griffith, W. P.; Marsden, S. P. Synthesis, 1994, 639. (d) Griffith, W. P. Chem. Soc. Rev. 1992, 21, 179]. Here, we report that ruthenium nanoparticles immobilized on hydroxyapatite is a superior catalyst for cis-dihydroxylation and oxidative cleavage of alkenes. With ethyl trans-cinnamate as a substrate, the supported catalyst has been recycled for successive cis-dihydroxylation reactions without significant deterioration of catalytic activities.
TABLE 1. provides representative examples of cis-dihydroxylation of alkenes catalyzed by ruthenium nanoparticles.
TABLE 2. provides representative examples of oxidative cleavage of alkenes catalyzed by ruthenium nanoparticles.
TABLE 3. provides representative examples of oxidative cleavage of α,β-unsaturated alkenes catalyzed by ruthenium nanoparticles.